The invention which is the subject of this application relates to improvements to the form and operation of magnetrons which can be operated for the sputter deposition of material from a target of said material when said magnetron is activated.
The sputtering of material targets from magnetrons is a well-known process for applying relatively thin, fine coatings onto substrates which are provided in proximity to said magnetrons. The coatings are compiled from the sputtered material and, if required, can be reacted with a gas plasma to provide a coating of required form. Furthermore, a plurality of magnetrons, having different target materials can be provided to be operated to form a multilayered coating of different materials on said substrates if required. There are many potential uses for the sputtering process such as, for example, the sputtering of coatings onto ophthalmic lens, light bulbs, semi-conductor devices, windows, compact discs and the like.
A problem with conventional sputtering magnetrons is the contamination of the targets of the material to be sputtered. This contamination can cause a build up of low energy back scattered material, i.e. material which is not successfully applied to the substrates to be coated, such as, for example, oxidised material on the surface of the target. Once the build up has reached a certain extent, the material can start to flake off the target during operation of the same and this flake material causes contaminants to fall from the target during operation onto the substrates and cause imperfections in the coatings formed which can mean that the substrates may have to be destroyed thereby adversely affecting production yield.
A further problem caused by the contamination is that arcing can occur between the contaminated areas of the target during operation and this arcing causes reduced efficiency of operation and can prevent the formation of coatings to the required consistency and quality.
Conventional magnetrons are typically provided with an array of magnets which comprise, for example for a circular magnetron, an annular array to the rear of the target and a centrally positioned magnet to the rear, with reverse polarity to the magnets in the annular array. Thus, all of the magnets are mounted behind the target in the magnetron body. The purpose of the magnets is to create a magnetic field across the surface of the target which causes sputtering of the target material when the magnetron is operated however, it is found that with this conventional magnet array, uneven erosion occurs on the surface of the target material which is being sputtered due to uneven strength of the magnetic field created across the surface of the target from which the material is sputtered. Thus, typically, the target material will be heavily eroded in an annular path where the magnetic field is strongest and straight, the outer limits of which are defined by the position of the magnets in the annular array and the inner limits of which is determined by the position of the centre magnet. The portion of the target material outside of this annular path is not eroded to the same extent, if at all, and it is in these areas that contamination and oxidation occur. Thus, the erosion across the surface of the target material is not uniform and hence wastage of material occurs and a reduction of the target material utilisation occurs.